Mat 329/330

This PR adds patches for a couple of issues:
 * Removes all caching of the JNI environment pointer. Even though the actual execution using the pointer was safe via the ordering in which it was performed, it was rather confusing. Removing the cache and always obtaining a local JNIEnv pointer regardless of context means the code is much clearer at the cost of a tiny loss in performance.
 * Disables tests that rely on the impairing of `AttachCurrentThread()` to break the `getEnv()` mechanism, all `JNIEnv` calls now go through the `getEnv()` function now, including those which are statically initialised. Therefore causing impairment to the `AttachCurrentThread()` function breaks the initialisers before the code to be tested can be run.
 * Deletes a local ref that escaped. There's no harm in leaving it but might as well keep things clean if possible.

Coverage:
Java: 91% (no change)
build/src/jshim 0.8% (no change)
build/src/librdag 16.1%  (no change)
src/jshim 57.6% (down 0.3%, due to method removal)
src/librdag 91.8% (no change)
src/librdag/runners 79% (no change).